Due to their long service life and low power consumption, LEDs are gaining attention as backlights for liquid-crystal display devices. In recent years, in addition to being used as liquid-crystal display devices for mobile phones, they have begun to be used as liquid-crystal display devices for TVs. In a backlight panel that uses LEDs, red, green and blue LEDs are provided on a substrate, and by lighting the LEDs for each color at the same time the three colors are combined to create white light.
While each LED is lit, the emission intensity for each color can be changed by repeatedly turning them on and off rapidly at a fixed frequency and changing the on/off ratio or the value of the constant current that flows while they are lit. An optical sensor for red, an optical sensor for green, and an optical sensor for blue are provided on the substrate, and when each LED is lit and the white light that is produced is incident on each sensor, each optical sensor measures the intensity of the light for each color, red, green, blue, and the emission intensity for each color is adjusted to obtain natural white light.
However, in addition to cases in which the emission intensity is reduced due to deterioration, there are cases in which the peak intensity wavelength (the peak wavelength) of the emitted light of an LED shifts due to temperature changes during use. When the wavelength shifts, the precise light intensity cannot be detected with an optical sensor, the sensitivity of which is adjusted for each color, the emission ratio for each color cannot be adjusted, and white light cannot be obtained; thus, a solution is desired.